We are studying calcium tracer flux, distribution, content, and ionized cytoplasmic calcium during monocyte activation. A model of monocyte calcium is being developed from 45Ca uptake and exoduscurves which indicates that cell calcium is partitioned between three compartments. The magnitude of the time constants for each pool suggests that there may be anatomical correlates of three compartments: a surface plasma membrane pool, a cytoplasmic pool, and an organelle pool. 45Ca uptake and exodus experiments are analyzed using a non-linear least squares fit of compartmental exchanges rates and sizes. The production of superoxide is used as a reflection of the state of activation of the monocytes treated with Concanavalin A. Con A-treated monocytes have an increase in the calcium exchange rate with the cytoplasmic pool from 0.04 to 0.07 min-1 (p less than .05), and an increase in the size of the cytoplasmic pool from 0.08 to 0.13 pmoles/cell (p less than .05). There are no significant changes in the exchange rates or sizes of the other two compartments. The cytoplasmic ionized calcium is measured with the fluorescent probe, Quin 2, which indicates a resting level of 83 nM free calcium in unadhered monocytes. Con A stimulation causes a doubling of the cytoplasmic free calcium to 163 nM within 45 seconds. The increment in cytoplasmic free calcium invariably precedes the onset of superoxide production after Con A treatment. These studies indicate that Con A binding to the plasma membrane increases the monocyte plasma membrane permeability to calcium. External calcium enters the cell at an increased rate and contributes to both internally-bound and free calcium. The magnitude of the increase in free calcium is proportional to the concentration of Con A and stimulates calcium extrusion via the calcium transport ATPase. Moreover, there is an increased concentration of ionized cytoplasmic calcium which has the potential to interact with other cellular regulators that modulate cell activation and superoxide production. (A)